Industrial gas turbines have a combustion section typically formed by an annular array of combustors. Each combustor is a cylindrical chamber which receives gas and/or liquid fuel and combustion air which are combined into a combustible mixture. The air-fuel mixture burns in the combustor to generate hot, pressurized combustion gases that are applied to drive a turbine.
The combustors are generally dual mode, single stage multi-burner units. Dual mode refers to the ability of the combustor to burn gas or liquid fuels. Single stage refers to a single combustion zone defined by the cylindrical lining of each combustor.
Stabilizing a flame in a combustor assists in providing continuous combustion, efficient generation of hot combustion gases and reduced emissions from combustion. For multi-tube premixers it is desirable to closely pack the tubes to minimize the recirculation zones at the exit plane and provide a practical air-side effective area. Multi-venturi tube premixers are one example of multi-tube premixers.
U.S. Pat. Nos. 4,845,952 and 4,966,001 disclose a multiple venturi tube device that employs a plurality of closely spaced parallel venturi tubes disposed in a pair of spaced-apart header plates. The venturi tubes are brazed to the header plates and the perimeters of the header plates are sealed to form a plenum into which pressurized gaseous fuel is supplied. The venturi tubes are arranged in a circular pattern that creates numerous large and irregularly shaped recirculation zones at their exit plane. These large and irregular recirculation zones result in poor flame holding resistance at the exit of the premixer.
U.S. Pat. No. 7,093,438 disclose a gas fuel injector includes a first header plate; a second header plate spaced downstream from the upstream header plate; and a plurality of venturi tubes arranged in rows and sealably secured to the first and second header plates. Each of the venturi tubes includes an inlet section, a throat section and an exit. The exit is shaped into a pattern that reduces space between each of the venturi tubes at the exit of each of the plurality of venturi tubes.